A Koenig Born diagram is a diagram used to remember the Maxwell's relations. In the figure below , U stands for Internal Energy, H for Enthalpy, G for Gibb's free energy, and A for the Helmholtz free energy, V is Volume, P is pressure, T is temperature and S is entropy. These are arranged in a Koenig Born diagram as follows:

V     A     T

U           G 
    
S     H     P

In addition there is an arrow from S to T and from P to V.

The diagram is read as follows. For example the top row of the square would be read as dA is a function of dV and dT and dA=-PdV-SdT.
The coefficient of dV is -P because the arrow links V to P and the connection goes against the arrow.Similarly the coefficent of dT is S because the arrow links T to S and the the minus sign is because the connection goes against the arrow.